Field of the Invention
The invention relates to applications in the field of mass spectrometry. In order to measure substances of interest mass spectrometrically, they must be transferred into the gaseous phase, unless they are already gaseous, and ionized. For sample substances which are originally liquid or solid, in particular, the ions are preferably produced with an ionization method which uses laser desorption, especially matrix assisted laser desorption/ionization (MALDI).
Description of the Related Art
Since being developed in the 1980s, MALDI has brought about crucial advances in the mass spectrometric analysis of large molecules and polymers as well as biopolymers, for example peptides and proteins. In this field, it is common practice to couple a MALDI ion source with a time-of-flight mass spectrometer (TOF) as the mass analyzer. MALDI-TOF mass spectrometry exhibits a high level of sensitivity and is particularly suitable for large and complex molecules, which is of great importance for applications in biology and for chemical analyses.
As the specialist is well aware, MALDI is based on the co-crystallization of a matrix substance and the analyte of interest in the sample with a molar excess of matrix molecules of 102 to 105. During the growth, the analyte molecules embed themselves into the crystals of the matrix substance. Usually, successful co-crystallization requires a ratio of analyte molecules to matrix molecules of around 1/5000 (mol/mol). Small organic molecules that strongly absorb energy at specific laser wavelengths, for example at 337 nanometers for nitrogen lasers, are often chosen as the matrix substance. Sinapic acid, 2,5-dihydroxybenzoic acid and α-cyano-hydroxycinnamic acid can be named here as examples. The excitation is performed using short, high-energy laser pulses of, for example, two to five nanoseconds' duration. After relaxation in the crystal lattice, the excitation leads to the explosive transfer of small amounts of substance on the surface of the matrix crystal into a hot plasma. The embedded analyte molecules, together with the matrix, are transferred from the ion source into the vacuum of the mass spectrometer and thus become accessible for mass spectrometric analysis.
An essential part of a MALDI-based mass spectrometric measurement is the sample preparation and the application onto the sample support. The person skilled in the art is familiar with different methods, such as the so-called dried droplet method, which ultimately comprises the mixing of an analyte solution and a matrix solution with subsequent vaporization of the solvent used, or so-called thin layer preparation. Several means of sample preparation have been described in the past and are known to the person skilled in the art. One example to mention here is the brochure published by the applicant in Sep. 2012 entitled “Bruker Guide to MALDI Sample Preparation”, in which different types of sample support plates and a selection of possible matrix substances are presented.
The previous patent applications by the applicant DE 196 28 112 A1 (corresponding to GB 2 315 328 A and U.S. Pat. No. 5,841,136 A) and DE 196 28 178 C1 (corresponding to GB 2 315 329 A and U.S. Pat. No. 5,770,860 A) disclose an introduction port for flat sample supports into the vacuum system of a mass spectrometer, said introduction port comprising an evacuable cartridge for receiving the sample supports, and a method for rapidly and simultaneously applying a large number of samples in solution from microtitration plates to a MALDI sample support plate. Both documents mention in passing that some sensitive sample substances are preferably applied to the sample support under a protective gas.
The U.S. Pat. No. 6,508,986 B1 (Anderson et al.) describes an alignment plate designed in the form of an aperture mask, whose arrangement of apertures corresponds to the sample site array of a MALDI sample support plate positioned underneath it and serves to guide the pipette when sample substances are being applied.
The international publication WO 2015/074959 A1 discloses a nebulizing system with a closed chamber with controllable atmosphere in which MALDI sample preparations can be conducted in an inert gas atmosphere.
Given the information above, a need exists in the technical field to provide devices and methods with a not very complex protective gas system with which sensitive substances also can be applied to a sample support.